David Gibson- MA, PhD
- University of Exeter
David Gibson
- MA, PhD
- University of Exeter
2016 to 2023: Senior Research Fellow, University of Exeter (Camborne School of Mines) (Honorary position from 2021)
About
40
Publications
57,203
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80
Citations
Introduction
I have an MA degree in Maths/Engineering from Cambridge University and a PhD from the University of Leeds. From Jan 2016 to July 2023 I was a Senior Research Fellow at the University of Exeter's Camborne School of Mines where I studied resilient forms of radio communication using novel antennas and mesh networks. (The last 3 of those years were in an honorary post). See my archived staff profile at https://web.archive.org/web/*/http://emps.exeter.ac.uk/csm/staff/adwg201
Current institution
Additional affiliations
January 2016 - July 2023
Position
- Senior Researcher
Description
- See my profile at https://emps.exeter.ac.uk/csm/staff/adwg201 - saves me typing it all over again. If thats missing, see the archived copy at https://web.archive.org/web/*/http://emps.exeter.ac.uk/csm/staff/adwg201
Education
March 1996 - February 2003
October 1977 - June 1980
Publications
Publications (40)
{In Cave Radio & Electronics Group Journal 122 (ISSN 1361-4800), pp14-16. June 2023. Accessible via http://doi.bcra.org.uk/j122014.f }
An induction-loop transmitter can operate at a higher current than a grounded electric dipole because the loop has a relatively low resistance when compared to the resistance between two earthed electrodes. However...
Although through-rock radio is now well established, there are a number of puzzles that David Gibson asserts would benefit from further study.
{In Cave Radio & Electronics Group Journal 118 (ISSN 1361-4800), pp16-17. June 2022. Accessible via http://doi.bcra.org.uk/j118016.f }
David Gibson describes a term in optics and photography that is used to derive the range of distances – the depth of field – over which a subject remains in good focus. This does not, of itself, require restating h...
{In Cave Radio & Electronics Group Journal 117 (ISSN 1361-4800), pp22-24. March 2022. Accessible via http://doi.bcra.org.uk/j117022.f }. Stereoscopic pairs are traditionally viewed using a handheld 3D viewer. But when printed in a magazine or shown on a display board, such images are difficult to view unaided, as well as being necessarily very smal...
Letter to the Editor: It is suggested that an underground data transmitter could comprise a cylinder of compressed air operating a hammer via an electrical actuator. With the device sufficiently well coupled to the rock it might be possible to transmit a notable amount of sound energy. With the actuator controlled by a suitable data-modulator it co...
{In Cave Radio & Electronics Group Journal 117 (ISSN 1361-4800), pp16-18. March 2022. Accessible via http://doi.bcra.org.uk/j117016.f } Linear and rotary position encoders can measure position using a single-track binary sequence known as a chain code. In a follow-up to his article in CREGJ 116, David Gibson gives some further explanation of how ch...
{In Cave Radio & Electronics Group Journal 116 (ISSN 1361-4800), pp22-24. Dec. 2021. Accessible via http://doi.bcra.org.uk/j116022.f , plus 'part 2' and 'update' in subsequent journals. }. There are many examples, in electronic equipment design, where it is necessary to measure linear or rotary position, which is often achieved using an optical or...
David Gibson describes how the output pulses from two class-D double-sideband modulators using carrier-frequency PWM (CF-PWM) can be interleaved to create a class-D single-sideband modulation. The method, assumed to be novel, is simple enough to be implemented on a standard micro-controller, which means that it is more accessible to hobbyist design...
The British Cave Science Centre (BCSC) at Poole's Cavern in Derbyshire has been fitted with sensors and data loggers in support of a number of cave science projects. The sensors transmit their data to the Internet via a broadband telephone connection. Two data protocols are used, essentially a 'push' and a 'pull' operation, which David Gibson descr...
If you want to build a cave radio that extends the art and doesn’t just repeat earlier work, then David Gibson argues that SSB techniques are outmoded. Not only is DSB modulation simpler, but it offers additional opportunities – including receiving SSB signals, if that is still required. Expressly, Gibson suggests that trying to implement tradition...
In another of our ‘Fundamentals’ series, David Gibson explains why we use induction loops and grounded electrodes as cave radio antennas.
Further notes on energy harvesting and human-powered lighting. This article is an update to Gibson, David (2021), Energy Harvesting with Electrets, CREGJ 113, p16. March 2021.
Update: Battery Polarity Protector: Further to his notes on building rugged equipment, David Gibson describes a simple addition to a battery connector that prevents cells being inserted in reverse.
Update: Pressurised Enclosures : As a follow-up to his notes on building rugged equipment, David Gibson further describes the use of a pressurised enc...
David Gibson envisages a portable energy-harvesting device utilising a wristwatch-style automatic winder, with the mainspring driving an electrical power generator that uses an electret material. The mainspring provides a method of regulating the power transfer, not unlike the concept of ‘power matching’.
In an extension of his notes on regenerative braking, David Gibson describes how to build an LED lamp that is powered by a falling weight. This article is an update to Gibson, David (2020). Regenerative Brake Charges Your Caving Lamp Whilst You Abseil, CREGJ 110, p13–16. June 2020.
Voltage doublers and the Cockcroft-Walton voltage multiplier are examples of devices that use capacitors as charge-pumps to generate a high voltage at a low power in a relatively simple circuit. The conventional voltage multiplier is series-fed, acting as a 'bucket brigade' to pass the charge from one element to the next. This is difficult to analy...
Whenever a capacitor is charged, energy seems to go missing. This has consequences when designing equipment that makes use of capacitor charging, such as a charge pump. David Gibson explains the phenomenon and challenges the reader to say where the supposedly missing energy might have gone.
A caver abseiling down a pitch will lose potential energy, which is converted into heat in his abseiling device; but what if it were converted into useable energy instead? David Gibson explains the principles behind regenerative braking and how you might use the braking energy to charge a battery. However, this is for theoretical interest only, and...
In another of our 'Fundamentals' series, David Gibson describes the problems of building equipment for use in caves. Waterproofing is a big issue, but he also considers the choice of battery and some problems associated with switches and connectors. These notes are aimed at student electronic engineers who might be building equipment for use in cav...
Many textbooks and webpages quote a formula for the inductance of a thin wire hoop, but few actually give the derivation. David Gibson had been confused by formulas that appeared to differ by a factor of two but has eventually decided where the subtle difference lies. This leads to an interesting possibility for the design of a wideband loop antenn...
For cave radio applications, we are not normally interested in the radiation from a loop antenna because the distance over which we are working is small (relative to a wavelength) and so only near-field effects need to be considered. However, it is still interesting to consider the radiation field, and to express the radiation efficiency in terms o...
Inspecting abandoned mine shafts is critical in ensuring their safety through early identification of signs of deterioration. Since the common inspection methods of CCTV and LiDAR are not very effective underwater, two modules have been designed for inspecting the linings of flooded, abandoned mine shafts. Using sonar technology, they allow the ear...
This note demonstrates a rule that aids circuit design by allowing the component values around multi-input summing amplifiers or comparators to be easily calculated. It was first published 27 years ago in 1991 and again in 1993, in two relatively obscure journals. Now, in 2018, I have scanned and re-formatted the original text, because I still thin...
{In Cave Radio & Electronics Group Journal 93 (ISSN 1361-4800), pp8-9. March 2016. Accessible via http://doi.bcra.org.uk/j093008.f } The Discrete Fourier Transform is a well-established tool for obtaining a frequency spectrum from a set of sampled data. The coefficients obtained from the DFT are complex-valued and so both phase and amplitude can be...
{In Cave Radio & Electronics Group Journal 90 (ISSN 1361-4800), p9. June 2015. Accessible via http://doi.bcra.org.uk/j090009.f } Practical experiments with stereo pairs show that an adequate stereoscopic image can be formed by the human brain even when one of the images is considerably defocussed or pixelated. In a digital data transmission, the re...
{In Cave Radio & Electronics Group Journal 89 (ISSN 1361-4800), pp13-16. March 2015. Accessible via http://doi.bcra.org.uk/j089013.f } White LEDs are increasingly being used as sources of illumination for cave photography, both as modelling lamps and as alternatives to flashguns. Clearly, a simple way to determine the effectiveness of such illumina...
{In Cave Radio & Electronics Group Journal 88 (ISSN 1361-4800), pp13-14. December 2014. Accessible via http://doi.bcra.org.uk/j088013.f } With cave radio equipment, there has been a trend away from the use of induction loop antennas to the use of so-called earth-current antennas, i.e. long wires grounded at both ends. Both the HeyPhone and Nicola s...
{ In Cave and Karst Science 41(3) (ISSN 1356-191X), pp138-139, December 2014. Accessible via http://doi.bcra.org.uk/cks123138.f } Several methods of remotely measuring ground conductivity are known, which depend on measuring the amplitude and phase of a received signal, relative to its transmitter. All of these methods require the separate transmis...
The objective of this project has been to provide a resilient communications network infrastructure which meets operational and emergency needs of mine operators. The project has also studied a range of new technologies for mine evacuation and rescue. The research consortium involved three EU coal operators, two mine rescue services and five resear...
A brief letter commenting on previous correspondence from "self-trackers" who record aspects of their lives.
This book is a collection of essays on radiolocation in caves, and related topics. Most of the articles have previously been published in the journal of the Cave Radio and Electronics Group, a special interest group of the British Cave Research Association. The topic is approached from a theoretical point-of-view, studying the mechanism of propagat...
The ADEMA project comprised a programme of integrated research seeking to enhance
mining exploration and planning capability. The main topics studied were seismic
processing, radio imaging, drilling parameter analysis, micro-seismic activity and predictive
analysis.
{Available via http://www.lulu.com/spotlight/gardenshedpress/ } Sub-surface or through-the-earth communication using electromagnetic fields – and specifically magnetic induction equipment – plays a key role in search and rescue systems used in the mining industry and, increasingly, by cavers and pot-holers. Similar equipment is used for radio-locat...
In an application to measure subterranean radio propagation, a wide-band low-frequency channel sounder makes use of a modified
pseudo-random binary sequence with an imperfect (non-impulsive) auto-correlation function (ACF). The transmitting antenna
for this system is essentially an induction loop, and the extreme wideband nature of the system requi...
A method is described for compressing analogue speech waveforms to reduce the peak/mean
ratio without adversely affecting the speech intelligibility or acceptability. The software is relatively simple and
is suitable for implementation in a low-cost RISC microcontroller. Methods of testing the resultant intelligibility
using a diagnostic rhyme test...
The accuracy of a conventional cave survey, constructed using compass, clinometer and tape, and the treatment of the associated surveying errors has been well-discussed. Such surveys are sometimes "corrected" by means of radio-location; but the accuracy of radio-location techniques has not been widely debated. Properly understood, radio-location er...
Cave surveying currently relies on visually reading a compass and clinometer. The price of magnetometers and solid-state inclinometers is falling rapidly; thus an electronic compass/clinometer with automatic data-logging is now feasible at an affordable price. However, the interpretation of the readings needs to be done with care because if the ins...
Components tolerances are critical because even slight deviations from the required values give rise to noticeable increases in phase and amplitude error. Hence, most outphaser designs do not make any provision for trimming the component values. This paper studies the effects of component tolerances on outphaser performance and looks at multisectio...
In IEE Review, Sept 1990. Letters. The writer asks how long data on a floppy disc remains valid, and asks if any work been done to ascertain the relationship between the probability that a bit will be misread versus time in storage, temperature and ambient magnetic field. The writer wonders if the gradual realignment of the magnetic domains would h...
Low frequency sub-surface radio is used for communications with miners and cavers. The signal attenuation is dependent on frequency and on the electrical conductivity of the ground. In addition, the optimum frequency for communications is dependent on depth below the surface; and on the degree of noise and co-channel interference. An adaptive commu...
Questions
Questions (2)
I am trying to find a mathematical model of a loudspeaker in an enclosure. By this, I mean an equation that describes the electrical impedance of the speaker as a function of the physical characteristics of the cone and the air in its enclosure.
As an analogy, I am familiar with the model of a servo motor, which relates its electrical impedance to the inertia of the load and the shaft speed. You can read an article I wrote about that at https://www.researchgate.net/publication/355587208_Regenerative_Brake_Charges_Your_Caving_Lamp_Whilst_You_Abseil.
Interestingly, one of the terms in that expression is the inertia divided by the product of torque constant and voltage constant, which has the dimensions of capacitance, showing that a electrical model of a servo motor includes a large capacitance. I am looking for something similar for loudspeakers, which shows how the physical characteristics of the enclosure and speaker are reflected in its electrical circuit model.
I cannot find any information on the straightforward reaction that takes place in a heated solution of starch and sugar. I would like to know more about this reaction; preferably via references to textbooks or peer-reviewed papers, please, although it seems to be an obscure topic.
Presumably this reaction is not a hydrolysis of the starch - since that generally requires more aggressive conditions (see the process for creating modified starch) - but it must be something more than a mere gelatinisation, because gelatinisation is rapid and takes place below 100 C, whereas the reaction between starch and sugar is slow and requires a higher temperature.
A demonstration of the reaction: Prepare a solution of sugar (sucrose), boil it to 'soft ball' and then slowly pour it into a cold slurry of cornflour (a.k.a. cornstarch outside the UK) and water, to which a dash of cream of tartar has been added. Bring the liquid back to the boil and simmer very gently for several hours, stirring..
Result: With the sugar, the mixture starts out white and cloudy but, after some time, turns clear and golden. Without the sugar (but still with the cream of tartar) the mixture thickens, and remains white and opaque. The latter reaction is clearly just gelatinisation but, equally obviously, the former reaction with sugar must be something else. So what is happening?
I have consulted a couple of text books but the descriptions of the chemistry are vague and confused. On the one hand, the books state that starches have a gelatinisation temperature which can vary, but which is always less than 100 C. (The chemical process is described and it would seem clear that this process takes only a few minutes to achieve the thickening of a starch slurry as it is heated). But on the other hand, the books also say that the starch/sugar reaction (which they also call gelatinisation) is slow and can take several hours. Those two points would appear to be contradictory - the starch/sugar reaction is not (I assert) gelatinisation.
A further point is that there seems to be a distinction between 'thickening' and 'gel forming' ability of starch. It seems to be stated that starches that thicken well, will tend to form poor gels. However, I have not been able to find a reference that adequately confirms that, or explains the chemistry of those two related processes.
The effect of moderate heat and weak acid on sucrose is to hydrolyse or 'invert' it by splitting the sucrose (a di-saccharide) into dextrose and fructose (mono-saccharide); reducing sugars as they are known. This gives rise to my speculation that it is the reducing sugar that is reacting with the starch.
So, in summary...
1. What is this reaction between starch and sugar?
2. Is a mono-saccharide (i.e. a reducing sugar) necessary for the reaction with the starch?
3. The text books say that starches that thicken well, will tend to form poor gels. Why is this so?
